[LU-14510] FIEMAP does not work on DoM files

• Status: Open
• Project: Lustre
• Affects Version/s: Lustre 2.14.0, Lustre 2.12.6, Lustre 2.15.0
• Type: Bug
• Priority: Minor
• Reporter: Andreas Dilger
• Assignee: WC Triage
• Resolution: Unresolved
• Labels: DoM2, e2fsprogs
• Severity: 3

Description

Creating a DoM PFL file and then running "filefrag -v" on it (ioctl(FIEMAP)) does not work:

# lfs setstripe -E 1M -L mdt -E 16m -c 4 -E eof -c -1 /mnt/testfs/dom-pfl
# dd if=/dev/zero of=/mnt/testfs/dom-pfl2 bs=1M count=1
# filefrag -v /mnt/testfs/dom-pfl2
Filesystem type is: bd00bd0
File size of /mnt/testfs/dom-pfl2 is 1048576 (1024 blocks of 1024 bytes)
/mnt/testfs/dom-pfl2: FIBMAP unsupported

The "FIBMAP unsupported" message is a bit misleading, since it tries FIEMAP first, but falls back to FIBMAP if that doesn't work.

Issue Links

• is related to: LU-11848 filefrag/FIEMAP doesn't work for PFL ...

Comments

[Andreas Dilger]

One issue that we need to decide is what the "device number" should be for MDT components of a file? Currently, we use device "0..nnnn" to represent OST0000..OSTxxxx, so we would have to use some other numbering for the MDT. While this is a 32-bit number and we only allow up to 65536 OSTs, unfortunately the high 16 bits were already consumed by storing the component number for LU-11848 to handle PFL files.

Another option would be to use an extent flag like FIEMAP_EXTENT_DATA_INLINE to indicate the data is being stored on the MDS. Strictly speaking, the FIEMAP_EXTENT_DATA_INLINE flag indicates that the data is stored inside the inode, and at some point we may want to allow this with the inline_data feature, but it might be a convenient short-term hack. A better solution would be to have a new flag like FIEMAP_EXTENT_METADATA=0x40000000, but it has some chance of conflict with other flags in the future unless we can add some upstream functionality that also uses this flag.